1 - It changes the internal volume of the cabinet making the speaker no longer *tuned* via cabinet area.
2 - Whatever is in there is going to rattle much more than you would think, someone turns on the stereo the jig is up (so to speak).
3 - If the face isn't screwed down it will really sound like ass, if it is, how are you going to access your shit in a reasonable response time ?
Still circling the moronosphere eh ?